Contents
Water hardness is one of the most important criteria that determine its consumer properties. Forming insoluble mineral deposits on the inner surface of electrical appliances and industrial equipment, it leads to a deterioration in their performance. To assess the quality of water, the permissible limits of the indicator are established.
How hardness salts are formed
Water is a universal solvent. The composition of natural springs is formed depending on the type of terrain. Water with carbon dioxide dissolved in it penetrates the soil, passes through the thickness of geological rocks – gypsum, dolomite, calcite, erodes them, enriching itself with organic and mineral substances, metal ions. They constitute the total mineralization of water (TDS).
Among them, calcium and magnesium cations predominate, their total value gives the total hardness of the water. It is divided into two types:
- temporary (carbonate);
- permanent (non-carbonate).
The formula for total stiffness is:
Жо = [Ca2+] + [Mg2+] = Zhк + Zhnk
Carbonate hardness is due to the presence of bicarbonates Ca(HCO3)2 and Mg(HCO3)2. They are easily removed from the solution, forming an insoluble precipitate upon boiling. The second type of hardness determines the content of soluble salts in water that cannot be removed by heating. To eliminate permanent stiffness, various methods are used, which will be discussed later in the article.
Unlike underground sources, surface waters contain less salts, as they are constantly diluted by precipitation. The level of rigidity in them is a variable value. It reaches extreme values in winter, and decreases during floods. In groundwater, this indicator is more stable.
Units
Salt concentration is measured in milligram equivalents per liter: 1 meq/l = 20,04 mg Ca2+ and 12,16 mg Mg2+. In the international SI system, the indicator is expressed numerically in moles per meter3 (mol/m3). In our country, degrees of hardness are used, 1 ºF u1d 0,5 meq / l or XNUMX mmol / l.
Degrees of hardness are also used in other countries, but differ in numerical values:
- German degree of hardness 1ºdH = 10 mg/l SaO or 7,194 mg/l MgO;
- french degree 1ºfH = 10 mg/l CaCO3;
- English 1°C lark = 14,254 mg/l CaCO3;
- American 1 gpg = 17,12 mg/l CaCO3.
To switch to other units of measurement, it is more convenient to use another American unit – PPM (PPM), which is equal to 1 mg / l CaCO3. From here:
- 1ºdH = 17,9 ppm;
- 1ºfH = 10,0 ppm;
- 1 ºClark = 14,25 ppm;
- 1º gpg = 17,1 ppm;
- 1ºЖ = 50,05 ppm.
You can convert ppm into degrees of hardness ºЖ that are convenient for us with a converter. To move between degrees, you can use the scale:
1 ºЖ = 2,804 ºdH = 3,5 ºClark = 5,005 ºfH = 2,924 gpg = 50,05ppm.
Stiffness standards
According to the parameter of general hardness, water is distinguished:
- soft – up to 4 ºF;
- medium hardness – from 4 to 8 ºF;
- hard – more than 8 ºF.
The diversity of natural conditions in Russia does not allow establishing uniform standards of rigidity for all regions. Maximum Permissible Concentration (MAC) Ca2+ varies widely depending on local conditions.
However, drinking water standards do not differ much from those set by the WHO (World Health Organization). Since January 01.01.2014, 31954, GOST 2012-XNUMX has been in effect as a national standard in our country. It takes into account the main international standards for water quality and analysis methods. The standard applies to all underground and surface sources.
Table 1. Normative values of calcium and magnesium concentrations in drinking water
The composition of water, depending on the purpose, is regulated by a hardness scale:
- allowable indicator for tap water – 300 ppm or 6 ºF;
- the optimal value for natural reservoirs is within 400 ppm or 8 ºF;
- maximum permissible level of hardness – 500 ppm, 10 ºЖ;
- the concentration of salts, representing a danger to life – more than 500 ppm, > 10 ºF.
Particularly stringent requirements are imposed on water that is supplied to heating boilers at power plants – the total hardness index cannot exceed 0,05–0,1 meq/l.
How to calculate stiffness at home
Increased rigidity is not expressed by any external signs – smell, color, consistency. It is evidenced by:
- the formation of scale on the bottom of the kettle;
- poor foaming of detergents;
- white stains on the shower head in the bathroom.
The exact composition of water can only be known through analysis. But even at home, there is an easy way to determine the hardness of tap water with a small error of 1-2 degrees.
For the experiment you will need: a piece of laundry soap, a small amount of distilled water, electronic scales, a container, a cylindrical glass, a ruler.
- Finely grate 1 g of laundry soap and dissolve it in 3-4 tablespoons of slightly warmed distilled water. If there is no kitchen scale at hand, you can focus on the eye – half a teaspoon without a top.
- Pour distilled water into a glass of soap solution so that the height of the liquid column corresponds to the percentage of fatty acids indicated on the bar of soap. If 72%, then the height of the water column should be 72 mm from the bottom of the glass, but not from the surface of the table.
- Fill a container with 0,5 liters of tap water and, stirring gently, pour soapy water into it in a thin stream. First, flakes, bubbles will appear in the water, then a persistent white foam. It indicates that all the salts are already bound.
You can calculate the number of centimeters of water column poured into the container by subtracting the height of the remaining soap solution from the original:
hп =hи -hо,
where:
- hп is the height of the poured solution column;
- hи is the height of the water column of the initial soap solution;
- hо – the height of the column of the residue of the soap solution.
Each centimeter of the solution poured into the container corresponds to 2ºdH. The value is the same as the German hardness unit. For example, poured from a glass 4,6 см, which corresponds 9,2 dH.
To translate the results obtained into mg-eq / l, you can use the table, and for an accurate result – calculator.
| number | Degrees dH | Level of hardness | Indicator in mg-eq / l |
|---|---|---|---|
| 1 | 0 – 4 | Very soft | Until 1,4 |
| 2 | 5 – 11 | Upholstered | 1,8 – 4,0 |
| 3 | 12 – 22 | Average | 4,3-8,0 |
| 4 | 22 – 34 | Hard | 8,0-12 |
| 5 | More 34 | Very tough | above 12 |
You can get a more accurate result using electronic testers such as TDS-3. They analyze the water for hardness and acidity, displaying the results on the screen as PPM or pH. You can convert PPM units to ºЖ with a calculator.
If you want to get a detailed analysis of water in a well or a well, then this can be done with the “Well-1” set.
Another simple and inexpensive way to determine the quality of water is with test strips.
Water influence
On the human body
To date, there are no serious studies confirming the harmful effects of hard water on a living organism. But it is known that prolonged consumption of water with an increased level of hardness contributes to the development of urolithiasis. The body does not have time to remove excess trace elements, which leads to the appearance of urinary stones, kidney stones and deposits in the joints.
Water quality also has hygienic significance. Soap, reacting with calcium and magnesium salts, destroys the protective layer of the skin, causing irritation or allergies. Hair becomes dry and brittle.
At the same time, calcium and magnesium are important trace elements for human life:
- daily calcium intake is 1000 mg;
- magnesium – 400 mg.
The lack of these elements can cause serious disorders in the body. According to studies conducted by WHO, it has been noted that the consumption of excessively soft water leads to the leaching of salts from the body and changes in the water-salt balance. In regions with the use of soft water, it is noted:
- an increase in cardiovascular disease;
- an increase in the number of fractures in children and a decrease in the weight of newborns.
WHO indicates that the presence of salts in water should be considered a necessary condition for the normal functioning of the body.
For equipment
Hardness salts cause a lot of problems associated with the use of household appliances and industrial equipment:
- a layer of scale that forms on the walls of washing machines and dishwashers leads to premature failure;
- taps and shower heads clogged with limescale;
- insufficient foaming of the washing powder leads to its overspending;
- scale-covered pipes and heating elements increase power consumption and fail;
Scale on the heating element of the boiler leads to its combustion - precipitated salts reduce the permeability of pipes in water supply systems, reducing water pressure;
- insoluble compounds on the walls of radiators become a powerful heat insulator, reducing their heat transfer.
Too soft water has a negative effect on equipment, increasing the risk of pipe corrosion due to low alkalinity. Therefore, it is necessary to maintain the correct balance of water-salt composition.
Water softening methods
There are various ways to reduce stiffness. The choice is determined depending on the initial quality of water, its purpose and conditions of use.
Thermal method
Boiling is the easiest and most affordable way to eliminate carbonate hardness. It is suitable for small volumes of water that are used for domestic needs. However, the method does not eliminate all hardness salts, and the dishes will have to be descaled.
Filtration
Not so long ago, a water softener filter represented an impressive installation. Modern technologies and materials have made it possible to create compact cleaning systems that give softness to the water, which easily fit under the sink in the kitchen. Replaceable filter cartridges, in addition to water softening, remove odors and impurities. Proper selection of filters and timely replacement guarantee high-quality water purification from a water supply system, a well or a well. One of the modern integrated systems are filters “Barrier”.
Chemical methods
To precipitate hardness salts, special reagents are added to the water – slaked lime, soda, polyphosphates. The method is effective for industrial applications. Its main disadvantage is the need for further waste disposal. Water after such treatment is unsuitable for food purposes.
Ion exchange
Filtration through ion exchange resins is successfully used in industry. The principle is based on the replacement of alkaline earth metal cations with sodium and hydrogen ions in a column with a fine-grained backfill. Salt solution is used to regenerate spent resin. If the water hardness level changes, manual adjustment of the settings is required.
Physical Methods
These methods are based on the processes of electrodialysis, the action of ultrasound, and electromagnetic pulses. Hardness salts are transferred to a modified state, in which they do not crystallize into a solid precipitate, but form unstable compounds. The use of ultrasonic and electromagnetic waves additionally contributes to the exfoliation of existing scale.
Membrane method
This method of purification has another name – reverse osmosis. Water under high pressure is passed through a filter with microscopic cells and is completely cleared of chemical impurities, suspended particles, bacteria. The quality of the resulting water is close to distilled. For its use, additional mineralization is required. The disadvantage of the method is its high cost.
Сonclusion
When evaluating water quality, it is important to consider not only the level of hardness and the likelihood of scale formation, but also the corrosivity. A correct assessment will allow you to choose an effective set of measures for water treatment.